Art of cracking



July `14,` 1942. ELCQHERTHEL ART oF CRAGKING Filed ov. so, 1938 MKWTMJ.- H.. -H

Patented July 14, 1942 UNITED STATES ART OF CRACKING Application November 30, 1938, Serial No. 243,054

'i' QFFICE 2 Claims.

This invention relates to improvements in the manufacture of motor fuel gasoline of high antiknock value from higher boiling petroleum oils. This application is, in certain aspects, a continuation in part of my prior application filed March 25, 1933, Serial No. 662,699.

In carrying out the process of the present invention, a stream of high boiling petroleum oil, a gas oil character stock, is heated to a moderate cracking temperature, 880 F.-910 F. for example, under a substantial superatmospheric pressure, 200-800 pounds per square inch for example, the hot oil products of this heating operation are separated, under maintained pressure, into a vapor stream and a liquid stream, and the separated vapor stream and liquid stream are separately heated, under maintained pressure, to further the cracking initiated in the first heating operation. The separation of the hot oil products of the first heatingoperation into a vapor stream and a liquid stream is effected in a pressure separator from which these separated streams are forced through the further heating operations by the pressure maintained in the separator. Other petroleum stocks, particularly reduced crude oil and gasoline character stock, are introduced into this pressure separator. Such gasoline character stocks, or their lower boiling components, are subjected to cracking or recracking in the heating operation through which the vapor stream from the pressure separator passes. The higher boiling components of such reduced crude oil are subjected to cracking in the heating operation through which the liquid stream from the pressure separator passes, and any components of such reduced crude oil vaporized in the pressure separator are subjected to cracking in the heating operation through which the vapor stream from the pressure separator passes. The hot oil products of both further heating operations are separated into residual fractions and vapor fractions. Gasoline fractions and higher boiling fractions, forming separate products some of which are appropriate for further processing, are recovered from these vapor fractions by appropriate fractionation, and certain of these separate fractions are reintroduced into appropriate portions of the system for further processing, l

This invention provides, in this combined operation, several special features of operation which afford special advantages. According to this invention, lower boiling components, low boiling virgin gas oil stock for example, are separated from higher boiling residual components of reduced crude oil introduced into the pressure separator and the thus separated fractions of the reduced crude oil are then subjected to the differing cracking conditions appropriate to each of the two separate fractions In a combined operation for the production of low viscosity residual fuel oil, so-called viscosity breaking of the residual components of the reduced crude oil introduced into the pressure separator 'is effected in the heating operation through which the liquid fraction from the pressure separator passes, this heating operation being controlled to subject the liquid stock mixture to cracking conditions appropriate to effect such viscosity breaking, these conditions being not inconsistent with those appropriate for further cracking of the liquid stock derived from the hot oil products of the first heating operation. For example, the liquid stream from the pressure separator may be heatedto a moderate cracking temperature approximating 875 F.-925 F. under a pressure approximating 1GO-400 pounds per square inch. Also according to this invention, the vapor stream from the pressure separator is with advantage heated to a cracking temperature substantially higher than that to which the stream of stock is heated in the first heating operation and substantially higher than that to which the liquid stream from the pressure separator is heated in the heating operation through which it passes. For example, the vapor stream from the pressure separator may be heated to a high cracking temperature approximating 940 F.-1080 F. under a pressure approximating 1GO-100 pounds per square inch. The stock components making up the vapor stream from the pressure separator are of a character appropriate to be heated to such high cracking temperatures, provided the pressure separator is properly designed and operated to prevent substantial entrainment of residual constituents in the vapor stream. Such high cracking temperatures, applied to these stock components, produce gasoline of high anti-knock value. Also according to this invention, gasoline fractions produced by lower temperature cracking in the combined operation, and straight-run gasoline, may be introduced into the pressure separator and thus subjected to recracking, or so-called reforming in the heating operation through which the vapor stream from the pressure separator passes thus to improve the antiknock value of such gasoline fractions. Reduced crude oil and gasoline character fractions introduced into the pressure separator assist in effecting and in controlling the separation therein at the same time that such stocks are being introduced into the operation at this point with special advantages with respect to processing or further processing of the introduced stocks. If desired, the residual fraction, or tar, separated from the hot oil products discharged from the heating operation through which the liquid stream from the pressure separator passes may be concentrated or reduced to coke by direct heat exchange with hot oil products discharged at high temperature, upwards of 950 F., from the heating operation through which the yapor stream from the pressure separator passes. These several features of operation provided by this invention may be used in conjunction or separately as hereinafter described and claimed.

The invention will be further described in connection with the accompanying drawing which illustrates, diagrammatically and conventionally, in elevation and partly in section with parts broken away, one form of apparatus appropriate for practice of the invention.

The illustrated apparatus comprises a heating furnace a heating furnace or furnaces of three sections 2, 3 and 4, a pressure separator 5, a vapor separator 5, a vapor separator, concentrator or coking chamber 1, fractionating towers 8, 9 and I 0, condensers II, I2 and I3, receivers I4, I5 and I6 and coolers I1 and I8. 'Ihe pressure separator 5 and the vapor separator 6 are provided with tar legs to facilitate the maintenance within these receptacles of that minimum Volume of separated liquid necessary to maintain liquid discharge through connections |9 and 29, respectively. The receptacle 1 may similarly be provided with a tar leg when it is operated as a Vapor separator or concentrator. When this receptacle 'I is operated as a coking chamber, it is provided in duplicate with appropriate connections to permit intermittent discharge of the solid coke product from alternate receptacles without interfering with the continuity of operation. The operation of the fractionating towers 8, 9 and |0 is controlled, to separate as overhead products gasoline fractions of desired boiling range, -by regulated introduction of part of the condensed overhead product as a refluxing medium, by means of pumps 2|, 22 and 23 through connections 24, 25 and 26, respectively.'

In carrying out the process of the invention in the apparatus illustrated, for example: Crude oil, supplied through connection 21, is forced by means of pump 28 through heater la arranged in heating furnace I in which it is heated to a temperature of 600 F.'700 F. and from which it is discharged into tower 8 through connection 29. In this tower, operated under a pressure approximating 10-60 pounds per square inch, for example, the introduced crude oil is separated into a gasoline fraction taken off through connection 38, a gas oil fraction taken off through connection 3| and a reduced crude oil taken off through connection 32. A kerosene fraction may, if desired, be taken off as a side stream through connection 33. The gas oil fraction taken off through connection 3| -is forced by means of pump 34 through the heater 2a arranged in furnace section 2 into the pressure separator 5 through connection 35. The reduced crude oil, or part of the reduced crude oil, taken off through connection 32, is introduced by means of pump 35 into the pressure separator 5 through connection 31. Part of this reduced crude oil may also be introduced into the receptacle 1 through connection 38. A pressure approximating 60G-700 pounds per square inch for example may be maintained in the separator 5 and the stream of oil passing through the heater 2a in furnace section 2 may be heated-to a temperature of 890 F.-900 F. therein. The introduction into the pressure separator 5 of reduced crude oil through connection 31, and of gasoline character stock through connection 39 as subsequently described, may be regulated to maintain in the lower part of the pressure separator a temperature approximating for example '7 50 lik-800 F. The liquid stream discharged from the pressure separator 5, through connection |9, including at least the higher boiling components of any reduced crude oil introduced through connection 31, is forced, by means of the pressure maintained in the separator 5, through the heater 4a arranged in furnace section 4 into the vapor separator 6 through connection 48 and pressure controlling valve 4|. In this heater the liquid stream from the pressure separator 5 is heated, for example, to a temperature of 830 F.-910 F. under a pressure, as discharged from the heater, of 250-350 pounds per square inch for example. The hot oil products from this heater are released through valve 4| into the vapor separator 6, maintained for example under a pressure approximating -75 pounds per square inch. The temperature in this separator 6 is controlled by the regulated introduction of a refluxing medium through either or both of connections 42 and 43 to maintain a temperature approximating 650 lit-775 F., for example, in the lower part of the separator. The separated residual tar is discharged from the vapor separator 6 through connection 20 and the separated vapor fraction is discharged to the fractionating tower 9 through connection 44. This tar may constitute the fuel oil product of the operation and may be discharged, in whole or in part, through connection 63. The high boiling gas oil character fraction separated in the tower 9, and taken off through connection 45, is with advantage supplied, together with the gas oil character fraction taken off' from tower 8 through connection 3|, to the heater in the furnace section 2, a1- though either all or part of this gas oil fraction may be discharged through connection 46. Part of this gas oil character fraction taken off from tower 9 through connection 45 may also be introduced, by means of pump 41, into the pressure separator 5 through connection 31 as a supplementary control medium. The Vapor stream discharged from the pressure separator 5 through connection 48, including at least the lower boiling components of any gasoline character fractions introduced into the separator 5 through connection 39, is forced by means of the pressure maintained in the separator 5 through the heater 3a arranged in furnace section 3 into the receptacle 1 through connection 49 and pressure controlling valve 58. In this heater the vapor stream from the pressure separator 5 is heated for example to a temperature of 960 F.1020 F. under a pressure, as discharged from the heater, approximating 200-400 pounds per square inch, for example. The hot oil products from this heater are released through the valve into the receptacle 1. The conditions maintained in the receptacle 1 are determined by the use of this receptacle. If this receptacle is operated as a coking chamber, a relatively low pressure and a relatively high temperature are maintained therein, a pressure of 15-30 pounds per square inch and a temperature of 950 F.1000 F. or somewhat higher for example. If this receptacle is operated as a vapor separator, primarily to separate residual tar from the vapor fraction of the hot oil products discharged from the heater arranged in furnace section 3, it may be operated for example under a pressure approximating 45-'75 pounds per square inch and at a temperature approximating 650 F.-750 F. Operated as a concentrator, for example to effect further vaporization of components of the residual tar discharged from vapor separator 6 through connection 2i), it may be operated for example under a pressure approximating 45-75 pounds per square inch and at a temperature somewhat higher than those used when it is operated as a vapor separator. When operated as a vapor separator or as a concentrator, the temperature in the receptacle 'I is conveniently controlled by the regulated introduction of a cooling medium through connection 5l. Gas oil character fractions supplied through either connection 38 or connection 52 may serve this purpose. When operated as a coking chamber, all or part of the residual tar discharged from vapor separator 6 through connection 20 may be introduced into the receptacle 1 through connections 53 and 5I, and thus coked by direct heat exchange with the hot oil products discharged at a coking temperature from the heater arranged in furnace section 3. The separated vapor fraction is discharged from the receptacle 1 to the fractionating tower lil through connection 54. If the residuum is discharged as a liquid, it is discharged through connection 55; if the residuum is discharged as a solid, it is periodically removed after opening and steaming out the receptacle. The high boiling gas oil character fraction separated in the tower IB, and taken off through connection 56, may be introduced into the vapor separator 6 through connection 42, or it may be introduced into the receptacle 'l through connection 52 or it may be discharged through connection 5l. To the extent that this gas oil character fraction is introduced to the vapor separator B through connection t2, it is revaporized in this separator and recondensed with the high boiling gas oil character fraction separated in the tower 9, any residual components it may contain being separated in the vapor separator 6, and may thus be supplied to the heater arranged in furnace section 2, A furnace oil fraction may, if desired, be taken off from tower l as a side stream through connection 58.

The gasoline character fractions separated in the towers 8, 9 and l5 are collected in the receivers it, l and l5, respectively. The gasoline fraction collected in receiver I5 the product of the severe cracking conditions maintained in the heater arranged in furnace section 3 through which the vapor stream from the pressure separator 5 passes, is `normally of high anti-knock value and is normally superior in this respect to the gasoline fractions collected in the receivers I4 and i5. Either or both of these gasoline fractions Inay be cracked or recracked to produce a gasoline fraction of improved anti-knock value by introduction, through connection 39 and one or the other of connections 59 and Gil, into the pressure separator 5 to be revaporized therein and thus to pass with the vapor stream from the pressure separator through the heater arranged in furnace section 3. Thus, the total gasoline product, or the total cracked gasoline product, of the combined operation may be .taken from receiver I6 through connection Bl. The straight run gasoline product or such part of it as is not introduced into the pressure separator 5, is taken from the combined operation through connec tion 62.

In the apparatus illustrated, the three cracking heaters are shown as arranged in three sec- -tions of a single furnace. These three heaters may be arranged in three separate furnaces or they may be combined in one or two furnaces. Control is somewhat simplified by separating them, but efficiency is usually improved by combining them. When they are combined in a single furnace, the furnace must be appropriately designed to maintain the required conditions in each of the three separate heaters.

It will be apparent that the process of the present invention can be embodied in a variety of combined operations. In apparatus such as that illustrated for example, with crude oil supplied through connection 21, or with reduced crude oil supplied through connection 32 and gas oil supplied through connection 3| from separate sources, the operation can be carried on to produce, as distillate products, gasoline and, if desired, furnace oil and, as residual products, either or both fuel oil and coke, or fuel oil and a highly concentrated residual tar. The gasoline product of the combined operation may comprise straight run gasoline, a gasoline characteristic of moderate cracking and a gasoline characteristic of severe cracking, or it may comprise exclusively gasoline characteristic of severe cracking, or straight run gasoline and gasoline characteristic of severe cracking.

When the operation is carried on to produce fuel oil, a fuel oil product of improved viscosity, that is of reduced viscosity, is obtained in a particularly advantageous manner. The residual components of the crude oil, or reduced crude oil, are subjected to cracking conditions appropriate to effect this reduction in viscosity, but only after the separation of components vaporizing under the conditions maintained in the pressure separator. Then, diluting and diluted with the residual products of the moderate cracking of gas oil, these residual components from the crude oil are subjected to further cracking effective both to effect a reduction in viscosity and to produce additional cracked gasoline.

I claim:

1. In the manufacture of gasoline, the improvement which comprises separating a gasoline fraction, a gas oil fraction and a reduced crude oil from a crude petroleum oil, heating a stream of the gas oil fraction as a distillate to a mod-- erate cracking temperature under superatmospheric pressure, discharging the resulting hot oil products into a pressure separator maintained under superatmospheric pressure, forcing a vapor stream from the separator by the pressure maintained in the separator through a separate heating operation and heating the vapor stream to a high cracking temperature therein, forcing a liquid stream from the separator by the pressure maintained in the separator through another separate heating operation and heating it to a moderate cracking temperature therein, separating residual tar and a gasoline fraction from the hot oil products from the last mentioned heating, and introducing the gasoline fractions separated from the crude petroleum oil and from thehot oil products from the last mentioned heating and reduced crude oil into the pressure separator.

2. In the manufacture of gasoline, the improvement which comprises heating a stream of high boiling petroleum oil as a distillate to a high temperature under superatmospheric pressure, discharging the resulting hot oil products into a pressure separator maintained under superatmospheric pressure, introducing reduced crude oil into the pressure separator, forcing a vapor stream from the separator by the pressure maintained in the separator through a separate heating operation and heating the Vapor stream to a high cracking temperature therein, forcing a liquid stream from the separator by the pressure maintained in the separator through another separate heating operation and heating it to a moderate cracking temperature therein, separating a gas oil fraction from the hot oil products from the second mentioned heating, introducing this gas oil fraction into the hot oil products from the third mentioned heating and separating the residual tar and a gas oil fraction from this mixture, and supplying this last mentioned gas oil fraction to the first mentioned heating. EUGENE C. HERTHEL. 

